Col Martin van Nieuwenhuizen, acting Benoni SAPS station commander, said the female victim was allegedly standing outside her car waiting for someone whom she would escort onto the highway, towards Johannesburg.
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He said two pedestrians approached her and stabbed her at around 3pm.
They fled with her handbag, which contained cash.
Van Nieuwenhuizen said the assailants disappeared into a nearby underground pipeline.
He said the victim was transported to hospital.
A police helicopter was called to the scene.
No arrests have been made.
More information to follow.